BACKGROUND: Heart rate variability (HRV) is a marker of cardiac autonomic tone. Depressed HRV has been reported in patients with AIDS. We conducted this study to find out if HRV is depressed in human immunodeficiency virus (HIV)-positive individuals without AIDS. METHODS: We studied prospectively HRV by spectral analysis of short-term electrocardiography (ECG) monitoring in 21 HIV-positives (33+/-11 years) and in 18 healthy volunteers (31+/-9 years). None of the HIV-positives had any clinical evidence of autonomic or cardiac dysfunction. Echocardiography was also performed in HIV-seropositives to rule out left ventricular (LV) systolic dysfunction. All these individuals did not have any evidence of AIDS. RESULTS: Mean CD4+ lymphocyte count was 426+/-166/mm(3). The ejection fraction (EF%) of HIV patients was 62.4+/-6.4. The total power of HRV was reduced significantly in HIV-positive individuals (p<0.00001). All the components of HRV were reduced. CONCLUSIONS: HRV is reduced in HIV-seropositive individuals in early stages of infection as well without any clinical evidence of autonomic dysfunction. This may serve as an early marker of future global sympatho-vagal imbalance.